Papers by Keyword: Self-Assembled Monolayer (SAM)

Abstract: Bone-like hydroxyapatite (HA) coatings were fabricated on titanium implants by a self-assembled technique and biomimetic method. After titanium plates were oxidized in a mixture of H2SO4/H2O2, a hexadecanoic acid self-assembled onto titanium surfaces. Contact angles of water and tricresyl phosphate on the surfaces were measured to characterize the self-assembled monolayer (SAM) and confirm the presence of the functional group. The titanium plates with SAM were used to fabricate HA coatings. In the simulate body fluid (SBF) with and without bovine serum albumin (BSA), Ca2+ and PO4 3- ions could spontaneously deposit onto the titanium surfaces and form bone-like HA coatings. The morphology, component and structure of samples were examined by scanning electronic microscopy, X-ray photoelectron spectroscopy, X-ray diffraction and attenuated total reflection Fourier transform infrared spectroscopy. The results suggested that the SAM can induce the formation of the nano-HA coating with a network and microporous structure. For the biomimetical HA coating induced by HDA-SAM, BSA could modulate the growth of HA crystal and decreased the grain size.

Abstract: We have investigated selective deposition of Co thin films on the OTS-patterned glass surface by using μ-CP(Micro-Contact Printing) coupled with MOCVD(Metal Organic Chemical Vapor Deposition) method with Co2(CO)8 as a Co precursor. Co thin films in the thickness of 5-180 nm has been selectively formed on the glass surface in the presence of the OTS(Octadecyltrichlrosilane) monolayer at the temperatures 60-90
, at the pressure of 0.03-0.6 Torr. The self-assembled OTS monolayer on the surface passivates the surface hydroxyl(-OH), adsorption sites for Co precursors, and thus significantly increases the induction period to nucleate Co metals on the OTS monolayer, compared with on the bare glass. Lowering the temperature and the processing pressure is likely to increase the difference in the induction period for the two substrate surfaces and thus improves the selectivity. About 180 nm-thick Co thin film was selectively formed on the OTS-patterned glass at 70
, however, lowering the temperature to 60
decreased the thickness, which is attributed to the reduced growth rate of Co at the lower temperature. The Co thin films deposited at 60-90
and at 0.03-0.6 Torr have the resistivities of 10-20 μ4-cm and are free of contamination. Consequently, the low temperature process for the selective deposition of Co in the presence of the OTS monolayer can be utilized for a variety of applications including flexible electronics and semiconductor devices.

Abstract: A novel technique has recently been presented for depositing metal layers onto a SAM. This is demonstrated here for Pd and Pt deposits on a mercaptopyridine (4-PyS) SAM. The SAMcovered Au(111) electrode is immersed into the metal-ion-containing solution without potential control. As a result, metal ions, e.g., Pd(II) (respectively Pt(II)) adsorb on the surface by forming a complex with the pyridine species. Subsequently, the electrode is transferred to a metal-ion-free solution, where the adsorbed metal ions are reduced electrochemically to its zero-valent state. Upon reduction, monoatomic high metal islands were observed in STM. Angle resolved XPS measurements show unequivocally that the reduced metal resides on top of the SAM.

Abstract: A novel photochemical approach is presented to fabricate a silicon oxide (SiOx) layer, which we have named an “oxide nanoskin” (ONS), whose thickness is defined in the molecular-order of 1~3 nm. Through the chemisorption of a vapor phase organosilane and subsequent photooxidation using 172 nm vacuum ultraviolet (UV) light, an extremely flat SiOx layer without cracks or aggregates was formed on various polymer substrates. Owing to this ONS coating, the charge density and surface acidity of the polymer substrates became almost equal to those of a native oxide-covered Si (SiOx/Si) substrate. In addition, there was marked improvement in the durability of the hydrophilicity and in the micro-wear resistance of the polymer surfaces. Moreover, organosilane self-assembled monolayer (SAM) chemistry currently available for the treatment of inorganic glass and Si substrates could be similarly utilized. Well-ordered SAMs with a wide variety of terminal-end groups (e.g., trifluorocarbon or amino groups) could be fabricated even on inert polymer substrates, in a manner similar to their fabrication on SiOx/Si substrates. Furthermore, we demonstrated the site-selective deposition of metal oxide and metal films on polymer substrates using photolithographically micropatterned SAMs as microtemplates. Well-shaped microstructures were achieved only on the polymer substrates with the ONS layer. On the substrates without the ONS layer, pattern resolution degraded significantly and growth rate decreased, since both depended greatly on the SAM density and quality. Our ONS was very useful not only in forming highly ordered SAMs on the polymer substrates, but also in obtaining excellent pattern resolution, sufficient growth rate, and adhesion of the target materials.

Abstract: As a ceramic, silicon nitride (Si3N4) has been suggested as a biocompatible material in contact with bone. In another configuration, as a low pressure chemically vapor deposited (LPCVD) thin film, Si3N4 can also be used as the sensitive material in certain biosensor applications. With the latter in mind, the biocompatibility of such films was investigated after them being modified with silane based self-assembled monolayers (SAMs) bearing functional end groups of methyl (CH3), primary amine (NH2), and carboxyl (COOH) respectively. The SAM surface modifications provided a wide range of physiochemical properties including hydrophobic (CH3), hydrophilic (bare Si3N4), positively (NH2) and negatively charged (COOH). Specifically the cell adhesion and proliferation, as well as the levels of alkaline phosphatase activity and osteocalcin, have been evaluated using the human osteoblast-like MG-63 cell line. It was observed that attachment and spreading was pronounced on NH2 while suppressed on CH3. With time the cells grew to confluence on all chemistries, and the levels of osteocalcin normalized to total protein content varied as CH3 > Si3N4 > COOH > NH2, but without significant differences. The highest spontaneous alkaline phosphatase activity was observed from cells grown on Si3N4 substrata.

Abstract: The hydroxamate-based artificial siderophore that contains terminated-amine group was newly synthesized. This artificial siderophore formed stable complex with FeIII ion and high bio-activities. The FeIII-artificial siderophore complex was attached onto the glass substrate surface by stepwise self-assembling method. The obtained artificial siderophore-modified glass substrate adsorbed the Gram-positive bacterium Microbacterium. flavescens. The Gram-negative bacterium Escherichia. coli was not adsorbed. The artificial siderophore-modified glass substrates indicated the selective adsorption of microorganisms.

Abstract: Site-defined metal microstructure was fabricated on the pre-designed organic template via a surface modification of Si(100) wafer. Site-defined substrate with octadecyltrichlorosilane (OTS) was oxidized by AFM (Atomic Force Microscopy) at threshold voltage (Vo). Terminal group (-CH3) of OTS was changed into carboxyl group (-COOH). Then, locally modified monolayer surface was used to induce the site-selective self-assembly of different materials (organic, metal, and semiconductor), according to the predefined patterns. The target metal selected is copper ions for the feasibility examination of conductive metal line fabrication